"Antifa" is just the newest incarnation of those psychotic, cowardly "Black Bloc" anarchist douchebags that come to liberal protests (Where they are of course welcomed with open arms by their fellow lefties) for the deliberate purpose of picking fights with cops and conservatives and starting riots. They're notable for their dressing all in black, having horrible B.O. (Owing to their belief that deodorant use, regular bathing, and other forms of personal hygiene are for Nazis), and wearing those stupid bandannas over their faces that make them look like lobotomized Wild West bank robbers.
They wear those bandannas for three reasons: 1) To make it harder for police to identify and arrest them when they inevitably get violent and throw molotovs through windows, 2) To make it harder for their rich parents to recognize them in news footage of the riots and cut off their trust funds, and 3) To cover up the fact that most of them have hideously rotted teeth due to their love of crystal meth and aforementioned hatred of personal hygiene. All three reasons rooted in cowardice.
A notable old member of their ranks was James Holmes, aka the Aurora Movie Theater shooter.